ホログラフィックメモリーなどの次世代光学デバイス用材料の結晶成長でご活躍のGanesan Ravi 教授（Alagappa University, India）の来日を機に、下記の様に講演会を実施いたします。
会場：１１号館２階 T 会議室
講師：Prof. Ganesan Ravi (Head of Department of Physics, Alagappa University, India)
AN OPTICAL DEVICES USING THE GROWN CRYSTALS
Photorefractive effect based devices find applications in various technological fields especially in modulation and optical memories. To fulfill this accomplishment, organic and inorganic crystals of DAST, DKDP and LiNbO3 were grown by low temperature and high temperature solution growth methods.
The first part comprises the following: DAST single crystals were grown by slow evaporation method using allyl alcohol as a solvent for the first time. DKDP crystals were grown by precise cooling using heavy water as a solvent. Both crystals were free from hygroscopic nature and free from any visible defects. An increased solubility and growth rate and controlled cluster formation were observed by the systematic control of growth parameters. Electro-optic modulators were designed and fabricated after careful evaluation of the orientation of the grown DKDP and DAST crystals. The electro optic figure of merits and half wave voltages were measured for these crystals and in particular these measurements were done for DAST single crystal to the wavelength 632 nm for the first time. Audio and video modulations were successfully tested using DKDP modulator.
In the second part, near-stoichiometric LiNbO3 doped with slight Mn were grown from melts with different compositions by using the top seeded solution growth method under optimized temperature gradient, pulling, and rotation rates. Two-color holograms were recorded in these crystals by the use of a near-IR laser of 778 nm for writing and a UV laser of 350 nm for gating. The results show the crystal with composition closer to stoichiometry exhibits better two-color holographic storage performance. Dependences of two-color sensitivity and multiplication (M) number on gating and writing intensities have been studied. Significant improvements of sensitivity, M number and dark decay were obtained compared to the previously reported values. The experimental results can be understood reasonably based on the band structure of Mn dopant and small polaron levels as deep and shallow traps, respectively. The results show that nearstoichiometric LiNbO3 slightly doped with Mn is a promising candidate for two-color holographic recording.